Low-cycle fatigue of the light advanced materials

Low-cycle fatigue (LCF) of 6061-T6 Al alloy plated with nickel, gold and silver as well as thermally-cycled carbon-epoxy laminate was studied at constant strain in a purely bending mode. The tensile and fatigue properties of the alloy coated with multi-layered deposits depend on the thickness of the inner electroless nickel layer that drastically decreases the ductility of the system. Electroplating by the second ductile Ni layer increases the lifetime of the alloy in comparison with that coated only by the electroless Ni layer. Thermal cycling of the carbon fiber reinforced polymer (CFRP) composite at maximum and minimum operating temperatures of 180°C and -195.8°C, respectively, shortens the fatigue life of samples in the high-cycle fatigue range corresponding to the number of cycles N exceeding 20,000. However, in the low-cycle fatigue region, the fatigue life of thermally-cycled laminates was slightly longer than that of the reference one, probably, due to the stress distribution between small cracks, which retards the fatigue failure and prevents fast propagation of the main crack.